Removal Of Elemental Mercury Over V/Ce Loaded Catalysts In The Flue Gas Of Coal-fired Power Plants

Due to its adverse effects on human health and ecosystem, mercury emitted fromcoal-fired power plants has aroused wide public concerns and proven to be a majorcontributor of anthropogenic source, so mercury removal would be imperative afterdust removal, desulfurization and denitrification from flue gas. This work evaluatedmercury removal based on SCR catalysts in simulated flue gas, characterized thesecatalysts by BET, XRD, Hg-TPD, XPS and H₂-TPR methods, discussed mercuryremoval mechanism over CeO₂-WO₃/TiO₂catalyst, and investigated deactivationperformance and mechanism over V₂O₅-WO₃/TiO₂catalyst caused by alkali (earth)metals. In addition, field tests of mercury removal in two real coal-fired power plantsare also performed. Results of our work are as followed:90-95%of Hg0could be removed over V₂O₅-WO₃/TiO₂, CeO₂-WO₃/TiO₂and lowCe doped V₂O₅-WO₃/TiO₂catalysts respectively in simulated flue gas, and thesecatalysts also showed good resistance to SO₂and H₂O. It is also found that importantgas components, SO₂and NO could promote mercury removal efficiency because ofthe enhancement of surface Hg0adsorption correlated to the newly formed sulfateadsorption acid sites, while H₂O and NH3could inhibit mercury removal since surfacecoverage and competitive adsorption caused by H₂O and NH3based on Hg-TPDresults.Further investigations on BET surface area, XRD results demonstrated thatsurface characteristics were not the dominant factor for mercury removal; However,XPS and H₂-TPR studies demonstrated that high state species, such as V⁵⁺and Ce⁴⁺arethe main active components on the catalyst surface.Simulated poisoning experiments over V₂O₅-WO₃/TiO₂catalysts showed thatdeactivation effects caused by alkali (earth) metals were well associated with alkalinityvalue and doping amounts. Further investigations on BET surface area, XRD, Hg-TPD,XPS and H₂-TPR methods demonstrated that surface characteristics were not thedominant factor for the deactivation, while the decrease of Hg0adsorption and surfaceredox ability (Oα), and the formation of inactive metavanadate species could beresponsible for the deactivation performance and mechanism. The small scale tests of mercury removal in two real coal-fired power plantsshowed the catalyst products such as CeO₂-WO₃/TiO₂was more effective (5-10%)than commercial V₂O₅-WO₃/TiO₂catalysts. Mercury removal efficiencies wereinfluenced by metal loading, space velocity, gas components and other conditionsrelated to dust concentration in the flue gas, in which alkali (earth) metals componentscaused deactivations greatly as the previous experiments.